Information about cardiovascular status, such as blood oxygen saturation, heart and respiratory rates can be unobtrusively acquired by photoplethysmography (PPG) using sensors such as contact sensors or remote sensors such as a camera. A PPG technique using a remote sensor is also referred to as remote PPG.
Whether using contact sensors or remote sensors, the PPG technique is susceptible to motion-induced signal distortions, which are superimposed to the desired vital signal. Distortions of the signals ascertained by PPG also arise from motion of the subject. Motion artifact reduction in PPG data representing the detected PPG signals is a challenging task since the contribution of the motion components often exceeds the contribution of the desired vital signal by an order of magnitude. The artifacts lead to erroneous interpretation and degrade the accuracy and reliability of estimation of cardiovascular parameters.
In a number of studies the associated PPG setups were usually operated under conditions that required the subjects to be motionless. This drawback limits the capabilities of the technique in real application environments, e.g., hospital and sports.
US 2013/0070792 A1 discloses techniques for denoising of physiological signals. A signal (e.g., physiological signal) comprising at least two signal channels is decomposed using independent component analysis (ICA) into at least two independent components. Then, independent component (IC) denoising is applied to estimate which of the at least two independent components belongs to a signal space and which of the at least two independent components belongs to a noise space using a statistical metric associated with the at least two signal channels. A de-noised version of the signal is generated by preserving in the signal only one or more independent components of the at least two independent components belonging to the signal space.
WO 2014/020463 A1 describes a device and a method for extracting physiological information from electromagnetic radiation emitted or reflected by a subject. A data stream derived from detected electromagnetic radiation is received. The data stream comprises a first sequence of signal samples indicative of various spectral portions. The data stream is split into at least two deduced staggered sequences of registered signal samples. Each of the deduced staggered sequences represents a defined spectral portion and comprises indicative signal samples spaced in time. Artificial samples are generated under consideration of proximate indicative signal samples so as to at least partially replace blank spaces between the indicative signal samples. This way, a supplemented data stream is generated.
WO 2013/038326 A1 is related to a device and a method for extracting information from remotely detected characteristic signals. A data stream derivable from electromagnetic radiation emitted or reflected by an object is received. The data stream comprises a continuous or discrete characteristic signal including physiological information and a disturbing signal portion. The physiological information is representative of at least one at least partially periodic vital signal. The disturbing signal portion is representative of at least one of an object motion portion and/or a non-indicative reflection portion. A relevant frequency band of the data stream is split into at least two defined sub-bands, comprising determined portions of the characteristic signal, each of which represents a defined temporal frequency portion potentially being of interest. The sub-bands are optimized so as to derive optimized sub-bands, the optimized sub-bands being at least partially indicative of a presence of the vital signal. The at least two optimized sub-bands are combined so as to compose an optimized processed signal.
WO 99/32030 is concerned with artifact reduction in PPG by removing motion artifacts prior to digital processing. A method is disclosed, comprising the steps of emitting electromagnetic radiation at tissue at at least first and second different wavelengths, receiving the radiation at the different wavelengths after it has been transmitted through or reflected within the tissue, providing at least first and second signals which are a logarithmic measure of the received first and second radiation wavelengths and subtracting the second signal from the first signal, removing a DC component of the result of the subtraction and providing an AC component to digital sampling means, and processing the digital samples in order to provide a desired value representing a property of the tissue.
US 2002/0077536 A1 describes a method and apparatus for analyzing two measured signals that are modeled as containing primary and secondary portions. Coefficients relate the two signals according to a model. In one embodiment the method involves utilizing a transformation which evaluates a plurality of possible signal coefficients in order to find appropriate coefficients. Alternatively, the method involves using statistical functions or Fourier transform and windowing techniques to determine the coefficients relating to the two measured signals. The methods are used in blood oximetry measurements.